In the state of the art, several ways of determining the angular orientation of a magnetic field using the Hall effect are known. In many cases, it is sufficient to restrict to an orientation within a plane, i.e. to determine the angular orientation of a the projection of the magnetic field into that plane.
For example, it is known to use two orthogonally arranged Hall devices and convert their respective Hall voltages into a digital number using analog-digital converters. The angle representing the wanted angular orientation is then derived by calculating the inverse tangent (arc tangent, ATAN) of the ratio of these two numbers, wherein typically a digital controller such as a microcontroller computes the ATAN function using either a CORDIC algorithm or a lookup table.
This solution has several rather undesirable consequences. A relatively high amount of energy is consumed, since two analog-digital converters and usually also a microcontroller are involved. And a microcontroller generally introduces a time delay, and in particular, the time needed for initializing the microcontroller will add up to the delay. Furthermore, the microcontroller is software-controlled, and in some applications such as in aircraft industry, the use of software in a sensor system requires a special and relatively tough qualification procedure.
In order to be able to dispense with the analog-digital conversion of two signals, phase-sensitive systems have been suggested. They are typically configured in such a way that at the output of the sensors a sine signal is obtained the phase of which represents the angle to be measured. The advantage is that the signal can be fed to a simple phase detection circuit for obtaining the desired angle. Various methods for generating a signal the phase of which contains the desired angular information have already been proposed.
E.g., in EP 2 028 450 A2, the desired signal is generated by summing up the outputs of two orthogonally arranged Hall effect devices (one of the devices being inclined with respect to the other by an angle of 90°). For accomplishing this, the Hall effect devices are provided with bias currents of sine shape which have identical amplitudes and are shifted by 90° with respect to each other. The generation of the required sine wave currents is relatively challenging and costly, and if the phase shift is not exactly 90° and/or if the amplitude of the sine waves is not equal, the outputted angular information does not precisely reflect the magnetic field orientation.
Another method is disclosed in WO 2008/145 662 A1. Therein, it is suggested to provide a particular sensing structure which can be considered a circular vertical Hall device which naturally produces a sine wave output. From the sine signal, a PWM signal proportional to the angle can be readily obtained. The manufacture of the required special Hall device is relatively costly, and the time required for a measurement is relatively long.
It is desirable to provide an improved way of determining the angular orientation of a magnetic field projected in a plane.